It's misleading to call those unfunded liabilities. Most of that is Social Security and Medicare projected expenditures. Unlike true liabilities, those are not legally guaranteed. The government can reduce eligibility for those programs, reduce payouts, etc, without being in default, unlike say a state pension plan.
Comparing them against current assets is equally misleading. Say you plan to spend $2k on rent for the indefinite future. That's $24k per year, $240k per decade, etc. Are you insolvent if you don't have all that in the bank now? No, of course not. Those are ongoing expenses paid out of ongoing income.
The Medicare trustee estimates the unfunded liability of Medicare at $40 trillion over 75 years (the $123 trillion figure includes a Medicare estimate of twice that). Projected GDP over that period is $907 trillion.
Finally, there is nothing wrong with quantitative easing. The people that'll be hurt by inflation are by and large the same ones whose fault the current financial mess is (older people own most u.s. assets). The government will probably encourage inflation at some point to reduce the value of these expenditures as a percentage of GDP without making nominal cuts. I don't see a problem with that readjustment.